Brook has remained relatively untested in his three title defences.Getty

Kell Brook and Jessie Vargas have traded blows on social media with the former threatening to walk away from their proposed welterweight title unification fight unless an agreement is met soon.

Brook, 30, has defended his IBF welterweight title three times since his sensational victory over Shawn Porter in August 2014 but will face his toughest challenge yet in reigning WBO champion Vargas.

At the end of June, Vargas posted a picture of himself signing a contract for the Brook fight, but accused the Sheffield-born fighter of stalling on the deal. "The date for my next fight has been changed due to the fact that Brook is having troubled signing his end of the deal," he wrote on Instagram.

Vargas, 27, then appeared to flirt with the idea of abandoning the fight altogether to instead pursue a second fight with Timothy Bradley, the man who has inflicted his only professional defeat to date.

"He [Brook] doesn't seem to be interested in the fight from the looks of it. Next big fight that the fans would enjoy would be the Bradley rematch."

Brook however insists there is nothing holding up the fight, suggesting an official announcement can be expected soon. "Stop talking s**t Jessie Vargas. TR [Vargas' promoter Top Rank] have the terms (over three times your biggest purse) we are ready to knock you clean out."

California-born Vargas won the vacant WBO title after stopping Sadam Ali in the ninth in March this year. Brook last's bout also came in March in a comfortable title defence against Kevin Bizier in his hometown of Sheffield.